You know what? How's this for controversial; I actually think they should do that sort of thing a little bit more.
The Joker speech bubbles....yeah, that font and style's definitely not for everyone, but I do like the idea behind it; of using the unique visual tools of this medium to provide a enriched voice for their characters. I wonder who started that?
I'd like to see a tiny bit more of that. I want Superman's dialogue to have a different font than Clark Kent's. I want Black Canary, with her awesome vocal powers, to have a little zing in her speech bubbles, just to help get across the idea of her voice being her superpower; and maybe as Dinah alters her voice you can alter the font as well. Darkseid should have his own font; I'd even go so far as to suggest creating a brand new one that is unique to his dialogue alone.
I also enjoy it when a little art is put on the speech bubbles themselves. When a devil or demon or some other hell-bound thing has a little flame drawn into it's speech bubble it just makes me smile. Or when there's some color in the bubble, like how Neron's speech is always colored green.
And I don't care how insensitive it is or whether it's harder to read, I liked it when a character's accent was written into their dialogue with bad phonetic spelling.